It is well known that heat destroys microorganisms. The presence of moisture accelerates this destruction by denaturing or coagulation of the proteins making up the microorganisms. Most microorganisms contain sufficient water so that moderate heat alone, e.g. 80° C.-100° C., will destroy the microorganism. Many bacterial spores, on the other hand, contain substantially no water and require elevated temperatures in excess of 150° C. for their destruction where dry heat is used. Hence, the destruction of such organisms is generally carried out in the presence of steam in steam sterilizers.
There are two basic types of steam sterilizers (autoclaves)—a gravity displacement autoclave and a prevacuum type sterilizer. In the gravity displacement autoclaves, steam is admitted at the top or the sides of the sterilizing chamber and, because the steam is lighter than air, forces air out the bottom of the chamber through a drain vent. Gravity displacement autoclaves are primarily used to process laboratory media, water, pharmaceutical products, regulated medical waste, and nonporous articles whose surfaces have direct steam contact. For gravity displacement sterilizers the penetration time into porous items is prolonged because of incomplete air elimination. For example, decontamination of 10 lbs of microbiological waste requires at least 45 minutes at 121° C., because the entrapped air remaining in a load of waste greatly retards steam permeation and heating efficiency.
Prevacuum type sterilizers are similar to the gravity displacement sterilizers except they are fitted with a vacuum pump (or ejector) to ensure air removal from the sterilizing chamber and load before the steam is admitted. By removing air, nearly instantaneous steam penetration can be provided even into porous loads.
Bowie-Dick type air removal tests are used to detect air leaks and inadequate air removal in prevacuum sterilizers. In the Bowie-Dick test, a commercially available Bowie-Dick-type test indicator is placed in the center of a test pack consisting of folded 100% cotton surgical towels prepared according to a standard test method, such as those found in American National Standards Institute (ANSI)/Association for the Advancement of Medical Instrumentation (AAMI)/International Organization for Standards (ISO) 11140. The test pack is placed horizontally in the front, bottom section of a sterilizer rack, near the door and over the drain, in an otherwise empty chamber, and the sterilizer is tested. Successful air removal is verified by a uniform color change in the Bowie-Dick-type test indicator after exposure to saturated steam at 132° C. or 134° C. for 3.5 min±5 sec and/or at 121° C. for 15 min±5 sec.
Inadequate air removal can result in an inadequate sterilization process, since air that is not removed from the chamber can interfere with steam contact. Thus, the air removal test is performed each day the vacuum-type steam sterilizer is used, before the first processed load. The test packs can be prepared using freshly laundered cotton surgical towels. ANSI/AAMI/ISO 11140 requires that the towels to be folded to a size 250 mm±30 mm in one direction and 300 mm±20 mm in the other direction, and that the height of the test pack to be between 250 mm and 280 mm. Thus, preparation for the air removal test for users can be labor intensive, time consuming and cost prohibitive. Disposable air removal test systems including disposable test packs have been developed, but they are still costly and create waste from disposing test packs after each use.
Therefore, there is a need for an improved air removal test system that can provide indication for successful air removal in prevacuum type sterilizers.